DE 10 2013 002 895 A1 relates to a piston for a reciprocating piston internal combustion machine with a piston shaft, with a piston crown having a circumferential ring part, in which piston crown an at least partially circumferential cooling duct for receiving a cooling medium is provided, and with at least one duct element extending partially in the piston shaft and partially in the piston crown, wherein the at least one duct element is fluidically separated from the cooling duct, wherein a second cooling medium which is different from the first cooling medium for cooling of the piston at least in regions is received in the duct element. In order to avoid an undesirable escape of the liquid sodium out of the respective duct element, it is proposed here to close the respective opening with a ball. This is very complex and therefore costly. The imperviousness of each individual closure element must furthermore be ensured in order to prevent an undesirable escape of alkali metal into the combustion chamber of the internal combustion engine.
The chambers into which the alkali metal is incorporated are formed as duct-shaped elements which have a straight profile and extend in a skewed manner to one another. This means that the axes of the duct elements do not meet at any point within the piston as a result of the skewed arrangement to one another so that a separate closure element is also required for each duct element, as a result of which its mounting outlay is increased.
Hitherto, pistons had a plurality of deep bore holes coming from the shaft side, which deep bore holes have to be bored in a very complicated fashion (oblique countersinking and boring). Each bore was closed individually in a complex fashion. The closure was embodied as fit and closed with a weld seam as a result of the requirement to be gas-impervious. Such bores were often created manually as a result of the complexity.